OUTLINE: This is a dose-escalation, multicenter study. Patients are accrued into stratum 1 initially and into stratum 2 if stratum 1 closes due to dose-limiting toxicity of myelosuppression or diarrhea. Patients on anticonvulsants will be accrued into stratum 3 and must meet the eligibility criteria for the stratum that is open (stratum 1 or stratum 2). (Stratum 1 closed as of 2002-09-15).